1. Field of the Invention
This invention concerns a tension reducer, and in particular, a tension reducer used in a webbing retractor for use in a seat belt system with which an automobile vehicle is equipped.
2. Related Art
This type of tension reducer (webbing retractor) comprises two types of flat coil springs, i.e. a strong (large) flat coil springs and a weak (small) flat coil spring. One end of the weak coil spring is attached to a winding shaft, and the other end is attached to one end of the strong coil spring via a gear spring. The other end of the strong coil spring is fastened to a case (cover). The winding shaft, weak coil spring, gear spring and strong coil spring are therefore connected in series, and the winding shaft is urged in the webbing winding direction by these flat coil springs. A pawl lever is disposed in the vicinity of the gear spring so as to interlock with the gear spring and thereby prevent its rotation. This pawl lever acts in synchronism with a solenoid or with the opening and closing of a car door.
After a passenger has put on the webbing, the pawl lever is operated by the aforesaid mechanism so as to prevent rotation of the gear spring. The urging force of the strong coil spring in the webbing winding direction therefore ceases to act on the winding shaft, the webbing is pulled only by the weak coil spring. Accordingly, the passenger does not feel constrained when he is wearing the webbing. When the passenger releases the webbing, the pawl lever no longer prevents the gear spring from rotating. The urging force of the strong coil spring in the webbing winding direction then acts on the winding shaft, which rapidly winds up the webbing.
In a webbing retractor provided with such a tension reducer, however, when all the webbing is wound, the coils of the weak coil spring 60 are in close contact with one another as shown in schematically in FIG. 5. After the webbing is drawn out and the tension reducer is operating, i.e. when the rotation of the gear spring connected to the outer end portion 62 of this weak coil spring 60 is prevented by means of the pawl lever, the urging force of the weak coil spring 60 in the webbing winding direction acts on the winding shaft when the coils of the spring are tightly wound, this urging force being released by the rotation of the shaft.
In this case, as the urging force of the weak coil spring 60 is released while an inner end 64 of the spring 60 connected to the winding shaft is winding out in the direction X shown in FIG. 5, adjacent side wall parts 66 in the vicinity of this inner end 64 rub against each other causing noise and impairment of operating performance due to friction.